1. Field of the Invention
The invention relates generally to marine propulsion devices, such as outboard motors and stern drive units. More particularly, the invention relates to reversing transmissions for such marine propulsion devices and to arrangements for transmitting axial propeller shaft thrust to the marine propulsion device gearcase.
2. Reference to Prior Art
Prior reversing transmissions for marine propulsion devices are generally of four different types:
1. The clutch dog type.
2. The cone clutch type.
3. The ball clutch type actuated by a radially movable member.
4. The roller bearing type actuated by a member movable axially on the outer surface of the propeller shaft.
The dog clutch type of reversing transmission is probably the most widely used and includes a clutch dog or member which is splined to the outer surface of a propeller shaft for axial movement relative thereto between positions of meshing engagement between two axially spaced counter rotating bevel gears. The clutch dog or member is moved axially by means of a pin connection with a shifter shaft housed in a forwardly open axial bore in the propeller shaft. The clutch dog or member and the bevel gears have essentially square projections, called lugs, which engage with each other when the clutch member or dog is moved axially toward one of the bevel gears. Examples of such constructions are shown in U.S. Pat. Nos. 4,850,910 and 4,865,570. Another embodiment of the dog clutch type moves the clutch dog axially by means of an external craddle on the clutch dog, rather than by the pin and internal shifter shaft. Dog clutches are very susceptible to wear.
The cone type clutch is used primarily in stern drive units. In this type of reversing transmission, two mating cones are forced together with a force proportional to the driving torque. This clutch relies entirely on the friction between the cones to drivingly connect the bevel gears to the propeller shaft. One example of such a cone type clutch is shown in U.S. Pat. No. 3,269,497.
The ball type clutch employes a shifter shaft which radially outwardly displaces one or more balls from recesses in the propeller shaft and into engagement with associated cam surfaces in the inside diameter of an associated bevel gear. Torque is transmitted directly from the engaged bevel gear to the propeller shaft through the balls. One example of such a ball type clutch is disclosed in U.S. Pat. No. 4,789,366. The ball type clutch is susceptible to impact damage to the balls and other components. Accordingly, its principal usage is in relatively low torque applications.
A roller type clutch is disclosed in U.S. Pat. No. 3,882,814 and involves axial movement of a roller retainer between forward drive, neutral, and rearward drive positions.
Attention is directed to the following prior art United States Patents:
______________________________________ 1,076,030 E. A. Ford October 21, 1913 2,291,151 W. T. Dunn July 28, 1942 2,497,361 H. M. Kesterton February 14, 1950 3,269,497 K. A. Bergstedt August 30, 1966 3,481,436 E. A. Wilkowski December 2, 1969 3,854,560 Nishikawa, et al. December 17, 1974 3,882,814 W. J. Shimanckas May 13, 1975 3,919,964 M. W. Hagen November 18, 1975 4,789,366 G. B Hale December 6, 1988 4,850,910 Higby, et al. July 25, 1989 4,865,570 Higby, et al. September 12, 1989 ______________________________________